Rebrand TypeDef to AlkType in code, keyword strings, and docs

Rename all 19 JSON Schema custom keyword strings from "TypeDef:*"
to "AlkType:*" (e.g., "TypeDef:Struct" -> "AlkType:Struct")
across source, tests, and docs. This is a breaking change to the
schema format itself — existing schemas using the old keywords
must be updated.

Rename the Rust identifiers:
- TypedefEngine -> AlkTypeEngine
- TypedefError -> AlkTypeError
- TypeDefKind -> AlkTypeKind
- TYPEDEF_PREFIX -> ALKTYPE_PREFIX
- get_typedef_kind{,_loose,_loose_enum,_enum} ->
  get_alktype_kind{,_loose,_loose_enum,_enum}

Update error message strings ("unknown TypeDef kind" ->
"unknown AlkType kind"), 11 test function names containing
typedef_kind/to_typedef_error, and doc-comment prose ("TypeDef
kind" -> "AlkType kind", "typedef engine" -> "alktype
engine", "typedef schema" -> "alktype schema"). Fix the broken
docs/architecture/crates/typedef/ path references in source doc
comments to point at docs/architecture/ directly. Rebrand the
typedef:annotation test fixture and the "not-a-typedef" test
string to their alktype equivalents.

Update ~20 generic "typedef" prose references in the architecture
docs ("typedef is the binary struct engine", "use typedef",
"typedef limitation", "replaced by typedef", etc.) to alktype.
Rename TypedefEngine in the ADR-007 code example to AlkTypeEngine.

Preserve as provenance per the prior prose-rebrand decision:
typedef.ts references (external TypeBox source file),
docs/research/alknet-typedef/findings.md research citations,
/workspace/alknet-typedef-poc/ POC path, and the
"alknet-typedef:" research section headers in findings.

Build, 295 tests, and clippy all pass clean.

docs/architecture/README.md

@@ -6,7 +6,7 @@ last_updated: 2026-07-22
 # alktype
 
 The binary struct engine: a small Rust crate that takes a JSON Schema
-with `TypeDef:*` custom keywords and produces an offset map, read/write
+with `AlkType:*` custom keywords and produces an offset map, read/write
 functions, and validation — all driven by the schema. The schema is the
 format definition; the engine is generic.
 
@@ -15,10 +15,10 @@ format definition; the engine is generic.
 | Document | Status | Description |
 |----------|--------|-------------|
 | [overview.md](overview.md) | draft | Crate purpose, "schema is the format" principle, dependencies, consumers, scope boundaries |
-| [schema-layer.md](schema-layer.md) | draft | The 19 `TypeDef:*` kinds, jsonschema custom keyword integration, TypeBox interop, schema annotations |
+| [schema-layer.md](schema-layer.md) | draft | The 19 `AlkType:*` kinds, jsonschema custom keyword integration, TypeBox interop, schema annotations |
 | [layout-engine.md](layout-engine.md) | draft | Offset computation, the two layout modes (packed sequential vs aligned static), alignment, endianness, variable-length handling |
 | [data-access.md](data-access.md) | draft | Read/write functions, TUnion dispatch, field paths, zero-copy access, length-prefix reading |
-| [validation.md](validation.md) | draft | Custom keyword validators for all 19 `TypeDef:*` kinds, `TypedefError`, load-time vs access-time validation, `TypedefEngine` |
+| [validation.md](validation.md) | draft | Custom keyword validators for all 19 `AlkType:*` kinds, `AlkTypeError`, load-time vs access-time validation, `AlkTypeEngine` |
 
 ## Applicable ADRs
 
@@ -27,7 +27,7 @@ format definition; the engine is generic.
 | [001](decisions/001-alktype-purpose-scope-jsonschema-engine.md) | Purpose, Scope, and the jsonschema Engine | What the crate is/isn't; why jsonschema not a custom engine; "schema is the format" principle; scope boundaries |
 | [002](decisions/002-two-layout-modes-packed-vs-aligned.md) | Two Layout Modes — Packed Sequential vs Aligned Static | The most important architectural finding; when to use each mode; `LayoutBuilder`/`SequentialReader` vs `OffsetMap` |
 | [003](decisions/003-schema-annotations.md) | Schema Annotations — Endianness, Alignment, Encoding, TUnion Discriminators | Concrete JSON shapes for all schema-level annotations |
-| [004](decisions/004-error-handling-validation-strategy.md) | Error Handling and Validation Strategy | `TypedefError` enum; load-time build, access-time check; field-path-carrying errors |
+| [004](decisions/004-error-handling-validation-strategy.md) | Error Handling and Validation Strategy | `AlkTypeError` enum; load-time build, access-time check; field-path-carrying errors |
 | [005](decisions/005-int64-uint64-first-class-kinds.md) | Int64/Uint64 as First-Class Kinds | 64-bit integers (SFTP offsets, metatensor data_offsets); JSON precision caveat |
 | [006](decisions/006-reject-non-final-inline-length-prefixed-in-aligned-mode.md) | Reject Non-Final Inline Length-Prefixed Variable Fields in Aligned Mode | Prevents silent data corruption (inline variable data clobbering subsequent fields) |
 | [007](decisions/007-packed-mode-read-factory.md) | Packed-Mode Read API — Engine as SequentialReader Factory | `engine.sequential_reader()` returns an owned reader, not a reference |
@@ -43,7 +43,7 @@ format definition; the engine is generic.
 
 ## Key Design Principles
 
-1. **The schema is the format.** A JSON Schema with `TypeDef:*` custom
+1. **The schema is the format.** A JSON Schema with `AlkType:*` custom
    keywords is both the validation spec and the layout spec. No separate
    format definition, no separate parser, no separate validator. One
    schema, three uses: validate, compute offsets, access data. See
@@ -88,11 +88,11 @@ format definition; the engine is generic.
    [validation.md](validation.md) and
    [ADR-004](decisions/004-error-handling-validation-strategy.md).
 
-8. **Not a serialization framework.** The typedef engine is not a
+8. **Not a serialization framework.** The alktype engine is not a
    general-purpose serde replacement. It operates on raw byte buffers at
    computed offsets — no intermediate `Value` tree, no reflection, no
    dynamic dispatch per field. For JSON data, use serde. For binary data
-   with a known schema, use typedef. See [overview.md](overview.md) and
+   with a known schema, use alktype. See [overview.md](overview.md) and
    [ADR-001](decisions/001-alktype-purpose-scope-jsonschema-engine.md).
 
 ## References
@@ -106,5 +106,5 @@ format definition; the engine is generic.
   schema kinds (619 lines)
 - `/workspace/jsonschema/` — the jsonschema crate (v0.46.5, Draft 2020-12)
 - `/workspace/alknet-typedef-poc/` — the POC code (disposable)
-- `/workspace/@alkimiadev/typebox-rs/` — prior attempt, replaced by typedef
+- `/workspace/@alkimiadev/typebox-rs/` — prior attempt, replaced by alktype
 - `/workspace/@alkimiadev/alktype/` — prior attempt (the @alkimiadev/alktype prototype, a handler-registry pattern; not to be confused with this crate, which reuses the name but is backed by the `jsonschema` crate)